Building Management System 1

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Building Management System
Part IV
Dr. KTMU Hemapala

Intelligent Building and BMS
A building that uses both technology and process to create a facility
that is safe, healthy and comfortable and enables productivity and
well being for its occupants. An intelligent building provides timely,
integrated system information for its owners so that they may make
intelligent decisions regarding its operation and maintenance. An
intelligent building has an implicit logic that effectively evolves with
changing user requirements and technology, ensuring continued
and improved intelligent operation, maintenance and optimization.
It exhibits key attributes of environmental sustainability to benefit
present and future generations.”
Source: CABA’s
Convergence of Green and
Intelligent Buildings Report

Definition of Intelligent Building
Technologies
“ The use of integrated technological building systems, communications and
controls to create a building and its infrastructure which provides the owner,
operator and occupant with an environment which is flexible, effective,
comfortable and secure.”

Thermal comfort and minimum health requirement must be achieved by the basic controls
of AC system, while the optimal control of the systems aims at providing satisfied thermal
comfort and indoor air quality with minimum energy input

Management Level

& Servers
Automation Level

Communication

Or Gateways/ routers
Communication

Field Level

Communication

Agents for BMS Development
• Agents or Building Agents: An agent is anything (hardware/ software)
that percepts information from its environment through sensors
and acting upon that environment through actuators.

Percepts
Sensors

Agent

Environment

Actuators

Actions
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What are Sensors?
• American National Standards Institute (ANSI) Definition
– A device which provides a usable output in response to a specified measurand
Input Signal

Technical
Specifications
of
Sensors…
Range – operation Range
Sensitivity – how much will the input variable must change to produce an output
Linearity – if not linear , signal conditioning needed
Resolution - the ability of a sensor to see small differences in readings
Stability - another way of stating drift. That is, with a given input you always get the same output
Repeatability - This is the ability of a sensor to repeat a measurement when put back in the same
environment.
Hysteresis - A linear up and down input to a sensor, results in an output that lags the input
Drift - This is the low frequency change in a sensor with time
Response Time - The time constant of any sensor is defined as the time required for that sensor
to respond to 63.2 of it.
Accuracy - is the degree of closeness of measurements of a quantity to that quantity's actual
(true) value.
Precision - also called reproducibility or repeatability, is the degree to which repeated
measurements under unchanged conditions show the same results

Light Sensor
• Light sensors are used in cameras,
infrared detectors, and ambient
lighting applications
• Sensor is composed of
photoconductor such as a photoresistor, photodiode, or
phototransistor
I
p

+

n

V

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Magnetic Field Sensor
• Magnetic Field sensors are used for
power steering, security, and current
measurements on transmission lines
• Hall voltage is proportional to
magnetic field
• BMS security checking

• Easy to implement (few components)
• Works very well in controlled environments
• Sensitive to ambient light

time

30

IR Reflective Sensors
• Reflective Sensor:
–
–
–
–

Emitter IR LED + detector photodiode/phototransistor
Phototransistor: the more light reaching the phototransistor, the more current passes through it
A beam of light is reflected off a surface and into a detector
Light usually in infrared spectrum, IR light is invisible

– Susceptible to reflectivity of objects
– Susceptible to the distance between sensor and the object
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Modulated Infrared
• Modulation and Demodulation
–
–
–
–
–

Flashing a light source at a particular frequency
Demodulator is tuned to the specific frequency of light flashes. (32kHz~45kHz)
Flashes of light can be detected even if they are very week
Less susceptible to ambient lighting and reflectivity of objects
Used in most IR remote control units, proximity sensors

Ultrasonic Sensors
• Basic principle of operation:
– Emit a quick burst of ultrasound (50kHz), (human hearing: 20Hz to 20kHz)
– Measure the elapsed time until the receiver indicates that an echo is detected.
– Determine how far away the nearest object is from the sensor

• Ranging is accurate but bearing has a 30 degree uncertainty. The object can be located
anywhere in the arc.
• Typical ranges are of the order of several centimeters to 30 meters.
• Another problem is the propagation time. The ultrasonic signal will take 200 msec to
travel 60 meters. ( 30 meters roundtrip @ 340 m/s )
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Thermocouple
• A thermocouple is a temperature-measuring device consisting
of two dissimilar conductors that contact each other at one or
more spots
• Suitable for High Temperature applications

Biggest Problems of the sensors are the
Errors
Sources of error of Sensors
• Interchangeability: the “closeness of agreement”
• Insulation Resistance: Error caused by the inability to measure the actual
resistance of element.
• Stability: Ability to maintain R vs T over time as a result of thermal
exposure.
• Repeatability: Ability to maintain R vs T under the same conditions after
experiencing thermal cycling throughout a specified temperature range.
• Hysteresis: Change in the characteristics of the materials from which the
sensor is built due to exposures to varying temperatures.
• Self Heating: Error produced by the heating of the sensor element due to
the power applied.
• Time Response: Errors are produced during temperature transients
because the sensor cannot respond to changes fast enough.
• Thermal EMF: Thermal EMF errors are produced by the EMF adding to or
subtracting from the applied sensing voltage, primarily in DC systems.

Time Constant
• The Thermal Time Constant is a measurement of the time
required for the sensor to respond to a change in the
ambient temperature. The technical definition of Thermal
Time Constant is, "The time required for a sensor to change
63.2% of the total difference between its initial and final
body temperature when subjected to a step function
change in temperature, under zero power conditions".

Temperature Sensors
Sensor Type

Primary Use

Advantages

Disadvantages

RTD

General Purpose,
Air, Water, Steam

Very Accurate,
Interchangeable,
Stable

Relatively Expensive
, not very sensitive

Thermistor

High Sensitivity
Applications,
Chilled water
metering

Large Change in
Resistance for a
small change in
Temperature Sensitivity

Flow Sensor
In VAV system: the measurement of Air Volume
to the space
( Air Velocity (fpm) = 4005 velocity pressure )
fpm -feet per minute
Volume flow is usually measured in cubic feet per minute (CFM).
velocity pressure - the moving air acquires a force or pressure
component in its direction or motion due to its weight and inertia
It is measured in inches of water column (w.c.) or water gage (w.g.)
static pressure - In operating duct systems, a second pressure is always
present. It s independent of air velocity or movement. it act equally in
all directions
Total pressure- is the combination of static and velocity pressures
In HVAC Flow is mostly measure in pipe or Duct

Flow measurements

Flow Measuring is mostly done through Pressure Measuring but
not always

Total Pressure = Static Pressure + Velocity Pressure

Flow Sensor/meters
• Pitot Tubes

• Venturi Flow meter

Annubar

• Turbines

Flow Sensor/meters
• Vortex

Flow Sensor/meters
• Orifice Plate

• Hot Wire Anemometers

Electromagnetic Flow Meters
use a magnetic field applied to the metering tube, which results in a potential difference
proportional to the flow velocity perpendicular to the flux lines
The potential difference is sensed by electrodes aligned perpendicular to the flow and the
applied magnetic field.

https://www.youtube.com/watch?v=f949gpKdCI4

Ultrasonic Flow meters
• There are two main types of Ultrasonic flow meters:
Doppler and transit time.
• by averaging the difference in measured transit time
between the pulses of ultrasound propagating into and
against the direction of the flow
• by measuring the frequency shift from the Doppler effect
• https://www.youtube.com/watch?v=Bx2RnrfLkQg

Actuators…..
An actuator responds to the output signal from a controller and
provides the mechanical action to operate the final control device,
which is typically a valve, damper or switch. A wide range of actuators
is available and the chosen actuator must address the following
concerns:
1. • matching the mechanical requirements of the controlled device;
2. • matching the characteristics of the control system, especially the output
signal of the controller;
3. • being suitable for its operating environment.

Access Control System
An access control system is a system which enables an authority to control access to areas and

resources in a given physical facility or computer-based information system. An access control
system, within the field of Physical Security is generally seen as the second layer in the security of
a physical structure.
System Components

 Access Controller
 Card Reader
 Electromagnetic locks

 Door Contacts
 Emergency Push Button
 Exit Push Button

 Access Cards

Access Control Topology

Typical Access Control Door Wiring

Specification for Door Controller shall
contain,
 No. of doors it can controlled
 No. of records it can stored

 Type of readers can connect
 No. of events it can record (Memory capacity)

 Power supply voltage
 No. of Inputs / Outputs available

Locks and Keys
• There are two types of locks
– mechanical and electro-mechanical

• Locks can also be divided into four categories
– manual, programmable, electronic, and biometric

• Locks fail and facilities need alternative procedures for access
• Locks fail in one of two ways:
– when the lock of a door fails and the door becomes unlocked, that is a fail-safe
lock
– when the lock of a door fails and the door remains locked, this is a fail-secure
lock
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Mantraps
• An enclosure that has an entry point and a different exit point
• The individual enters the mantrap, requests access, and if
verified, is allowed to exit the mantrap into the facility
• If the individual is denied entry, they are not allowed to exit
until a security official overrides the automatic locks of the
enclosure

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Closed Circuit Television (CCTV)

Hidden CCTV cameras

post mounted CCTV

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Fire Safety
• The most serious threat to the safety of the people who work in the
organization is the possibility of fire
• Fires account for more property damage, personal injury, and death
than any other threat
• It is imperative that physical security plans examine and implement
strong measures to detect and respond to fires and fire hazards

111

Fire Detection and Response
• Fire suppression systems are devices installed and maintained to detect
and respond to a fire
• They work to deny an environment of one of the three requirements for
a fire to burn: heat, fuel, and oxygen
– Water and water mist systems reduce the temperature and saturate some fuels
to prevent ignition
– Carbon dioxide systems rob fire of its oxygen
– Soda acid systems deny fire its fuel, preventing spreading
– Gas-based systems disrupt the fire’s chemical reaction but leave enough oxygen
for people to survive for a short time

112

Fire Detection
• Before a fire can be suppressed, it must be detected
• Fire detection systems fall into two general categories:
– manual and automatic

• Part of a complete fire safety program includes individuals that monitor the
chaos of a fire evacuation to prevent an attacker accessing offices
• There are three basic types of fire detection systems: thermal detection,
smoke detection, and flame detection
– Smoke detectors operate in one of three ways: photoelectric, ionization, and airaspirating

• Installed systems apply suppressive agents, either sprinkler or gaseous systems
– Sprinkler systems are designed to apply liquid, usually water

– In sprinkler systems, the organization can implement wet-pipe, dry-pipe, or pre-action systems
– Water mist sprinklers are the newest form of sprinkler systems and rely on microfine mists

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Gaseous Emission Systems
• Until recently there were only two types of systems
– carbon dioxide and halon (compound containing carbon and halogen)

• Carbon dioxide clears a fire of its oxygen supply
• Halon is a clean agent but has been classified as an ozone-depleting
substance, and new installations are prohibited
• Alternative clean agents include the following:
–
–
–
–

Method:
•Each thermostat receives a steady flow of funds
•Periodically thermostats bid against each other
for access to the cooling or heating fluid

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Market based zone control
(Cutkosky et. Al. 1993)

Logic:
•Thermostat offers to sell if it receives more than it needs
•Thermostat offers to buy if it receives less than it needs
•Bid is based on deviation from set point
Action:
•A central system aggregates the bids, calculates closing point
and total volume
•Provides control signal to dampers based on closing point